1. Field of the Invention
The present invention pertains to a pressure support system that includes a low leak alarm and to a method of providing such an alarm, and, in particular, to a pressure support system, which provides positive pressure therapy to a patient via a single limb patient circuit, that includes an alarm indicating that the current system leak from the patient circuit via an exhaust port is below an acceptable level, which involves comparing a current system leak with an adaptive alarm threshold.
2. Description of the Related Art
Pressure support systems that provide a gas flow to an airway of a patient at an elevated pressure via a single limb patient circuit to treat a medical disorder are well known. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the airway of a patient to treat obstructive sleep apnea (OSA). It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient""s breathing cycle or varies with the patient""s effort to increase the comfort to the patient. It is further known to provide a positive pressure therapy in which the pressure provided to the patient changes based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea or upper airway resistance
Conventional pressure support devices typically include a pressure generator, for example, a blower, piston or bellows, that creates a flow of breathing gas having a pressure greater than the ambient atmospheric pressure. A patient circuit delivers the elevated pressure breathing gas to the airway of the patient. Typically, the patient circuit includes a conduit, i.e., a single lumen, having one end coupled to the pressure generator and a patient interface device coupled to the other end of the conduit. The patient interface connects the conduit with the airway of the patient so that the elevated pressure gas flow is delivered to the airway of the patient. Examples of patient interface devices include a nasal mask, nasal and oral mask, full face mask, nasal cannula, oral mouthpiece, tracheal tube, endotracheal tube, or hood. A single limb patient circuit further includes an exhalation port, also referred to as an exhalation vent, exhaust port or exhaust vent, to allow expired gas from the patient to exhaust to atmosphere. Generally, the exhaust vent is located in the conduit near the patient interface and/or in the patient interface device itself.
A concern in a single limb pressure support device is that the exhalation port remains open during use so that a sufficient amount of expired gas exhausts from the system. Complete or partial blockage of the exhaust port can occur, for example, by a buildup of secretions from the patient in the exhaust port. Blockage can also occur as a result of an external item, such as the patient or the patient""s bedding, covering the port. For example, a patient using the pressure support system at night to treat OSA might roll over during sleep so that the exhaust port is covered by the patient""s sheets, pillow and/or mattress and cause a complete or partial blockage of one or more of the exhaust ports in the patient circuit.
Conventional pressure support device attempt to mitigate this concern by designing exhaust ports that are difficult to block. For example, multiple flow paths may be provided so that if one path becomes blocked, another path provides the necessary exhaust function. Also, routine maintenance, such as daily inspection and/or weekly cleaning, are recommended to ensure the integrity of the exhaust paths. These techniques, however, have several disadvantages. For example, they may not be sufficient to ensure the continuity of the exhaust paths at all times during the patient""s therapy, are relatively time consuming, and place a significant burden on the user in requiring the user to perform the routine maintenance and to remember to perform the maintenance. In addition, these conventional techniques do nothing to warn the user that an exhaust port blockage has taken place at the time the blockage occurs.
Accordingly, it is an object of the present invention to provide a single limb pressure support device having an exhaust vent in the patient circuit and/or patient interface device and that does not suffer from the above disadvantages associated with conventional single limb pressure support devices. This object is achieved, according to one embodiment of the present invention, by providing a pressure support device that includes a pressure generator adapted to provide a gas flow, a conduit coupled to the pressure generator to deliver the gas flow to a patient, an interface device coupled to the conduit to communicate the gas flow to an airway of the patient, and an exhaust vent that provides a flow of exhaust gas to atmosphere from the conduit and/or the interface device. A first sensor detects the rate at which gas flows in the conduit, and a second sensor detects the pressure of gas at the patient. A control system receives the outputs from the first and second sensors and determines whether a current flow of exhaust gas passing through the exhaust vent is below an alarm threshold based on the first and second outputs and provides a third output indicative of this determination.
It is a further object of the present invention to allow the pressure support system to set the alarm threshold based on the specific conditions of that pressure support system, so that the alarm threshold is optimized for the current conditions of the pressure support system. This object is achieved, according to one embodiment of the present invention, by having the pressure support system enter a learn period in which at least one parameter associated with the pressure support system is monitored. This parameter, or a plurality of parameters, are used to set the alarm threshold. Thus, the present invention can set the alarm threshold taking into consideration the specific conditions of pressure support system, such as the introduction of a supplemental breathing gas, e.g. oxygen, into the system, and not produce a false alarm.
It is still another object of the present invention to provide a method of providing pressure support to a patient via a single limb circuit having an exhaust vent in that circuit and that does not suffer from the disadvantages associated with the above-described conventional single limb pressure support techniques. This object is achieved, according to one embodiment of the present invention, by providing a method of providing pressure support via a pressure support system, wherein the method includes the following steps: (1) providing a gas flow from a pressure generator to a patient via a conduit coupled to the pressure generator, wherein an interface device is also coupled to the conduit to communicate the gas flow from the conduit to an airway of the patient, and wherein an exhaust vent in disposed in the interface device or the conduit to communicate a flow of exhaust gas to atmosphere, (2) detecting a rate at which gas flows in the conduit, (3) detecting a pressure of gas at the patient, (4) determining whether a current rate at which exhaust gas passes through the exhaust vent is below an alarm threshold based on the detected gas flow and pressure, and (5) providing a third output indicative of a result of the determining step.
It is a still further object of the present to provide a method of setting the alarm threshold based on the conditions of the pressure support system so that the alarm threshold is optimized for the current conditions of the pressure support system. This object is achieved, according to one embodiment of the present invention, by monitoring the rate at which gas flows in the conduit and the pressure of gas at the patient during a learn period and setting the alarm threshold based on the monitored rate of gas flow in the conduit and the pressure at a patient during the learn period. Thus, the present method can set the alarm threshold to account for the specific condition of the pressure support system, such as the introduction of a supplemental breathing gas, e.g., oxygen, into the system and not produce a false alarm.
These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.